Method for encapsulation of electronic devices

ABSTRACT

An encapsulation for an organic light emitting diode (OLED) device is disclosed. The encapsulation includes a sealing dam surrounding the cell region of the OLED device to support a cap. Spacer particles are randomly located in the cell region to prevent the cap from contacting the active components, thereby protecting them from damage. The sealing dam provides a sealing region between the edge of the cap and dam in which an adhesive is applied to seal the OLED device. The use of the sealing dam advantageously enables devices to be formed with narrower sealing widths.

[0001] This application claims the priority of patent applications titled “Encapsulation of Organic LED Devices”, PCT/SG99/00143 (attorney docket number 99E02809SG) and “Sealing of Electronic Devices”, PCT/SG00/00133 (attorney docket number 99E05737SG).

FIELD OF THE INVENTION

[0002] The present invention relates to organic light emitting diode (OLED) devices. More particularly, the invention relates to encapsulation of OLED devices.

BACKGROUND OF THE INVENTION

[0003]FIG. 1 shows a conventional OLED device 100. OLED devices can be used as displays in various consumer electronic products, including cellular phones, cellular smart phones, personal organizers, pagers, advertising panel, touch screen displays, teleconferencing equipment, multimedia equipment, virtual reality products, and display kiosks.

[0004] The conventional OLED device comprises a functional stack of one or more organic functional layers 110 between a transparent conductive layer 105 and a conductive layer 115. The functional stack is formed on a transparent substrate 101. The conductive layers can be patterned to form one or more cells or pixels on the substrate. Bond pads 150 are coupled to the cathodes and anodes to control the OLED pixels. In operation, charge carriers are injected through the cathodes and anodes for recombination in the functional layers. The recombination of the charge carriers causes the functional layer to emit visible radiation.

[0005] A cap 160, which forms a cavity 145 between it and the pixels, is mounted on the substrate. A sealant 187 is applied around the edges of the cap where it contacts the substrate. However, due to the gap G that exists between the cap and substrate, the sealing width W needs to be sufficiently wide to prevent oxygen and moisture from permeating through the sealant. Typically, the sealing width is about 0.2-2 mm with a gap of about 0.01-0.5 mm. Such a large sealing width results in inefficient use of chip area, limiting miniaturization of OLED devices.

[0006] As evidenced from the above discussion, it is desirable to provide OLED devices having improved sealing and reduced chip size, particularly those formed on thin or flexible substrates to prevent mechanical damage of the active device layers.

SUMMARY OF THE INVENTION

[0007] The invention relates generally to OLED devices. In particular, the invention relates to the encapsulation of OLED devices. In one embodiment, a sealing dam surrounding the cell region of the substrate is provided. The sealing dam supports the cap on the substrate and provides a sealing region located at an outer face of the sealing dam. In one embodiment, the sealing region is located between the edge of the cap and dam in which an adhesive is applied to seal the OLED device. The use of the sealing dam determines the gap between the cap and substrate (thereby providing a cavity space between the diode and the cap for mechanical protection) and the sealing widths.

[0008] In addition, spacer particles are provided in the device region to prevent the cap from contacting the OLED cells. In one embodiment, the spacer particles are randomly deposited on the substrate by spraying techniques. The spacer particles are deposited, for example, by a dry spray technique. Alternatively, a wet spray technique is employed to deposit the spacer particles on the substrate. Spacer particles in the non-device region are removed, leaving the spacer particles randomly distributed in the device region. A cap is mounted on the substrate to encapsulate the device. The spacer particles in the device region prevent the cap from contacting the OLED cells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 shows a conventional OLED device;

[0010]FIG. 2 shows an embodiment of the invention; and

[0011] FIGS. 3-8 show a process for fabricating an OLED device in accordance with one embodiment of the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0012]FIG. 2 shows an OLED device 200 in accordance with one embodiment of the invention. The OLED device comprises a substrate 201 on which pixels are formed. In one embodiment, the substrate comprises a transparent substrate, such as glass. Other types of transparent materials that serve as a substrate to support the OLED pixels are useful. The OLED pixels comprise one or more organic layers 110 sandwiched between cathodes 105 and anodes 115. In one embodiment, the cathodes and anodes are formed as strips in respective first and second directions. Typically, the first and second directions are orthogonal to each other. The OLED pixels are formed in the cell region of the substrate. Bond pads 150 are electrically coupled to the cathodes and anodes. A cap 260 is provided to encapsulate the OLED pixels. The cap provides a cavity 145, separating the cap from the OLED cells. In one embodiment of the invention, spacer particles 680 are provided between the OLED cells and the cap. The spacer particles prevent the cap from contacting the OLED cells.

[0013] In accordance with the invention, a sealing dam 280 is provided on the periphery of the cell region of the OLED device to support the cap. The height of the sealing dam defines the cavity 145. In one embodiment, the sealing dam comprises a non-conductive material to prevent shorting of the electrodes. A multi-layered sealing dam in which at least the layer in contact with the substrate comprises a non-conductive material can also be used. The sealing dam forms a sealing space or region 285, which abuts an outer face 281 of the sealing dam. In one embodiment, the sealing dam is located a distance from the edge of the cap, leaving a sealing space 285 between the edge of the cap and the dam. A sealant 287 fills the sealing space, hermetically sealing the device. The use of a sealing dam advantageously eliminates the gap (gap G in FIG. 1) that exists in conventional encapsulations. This enables devices formed with narrower sealing widths, for example, <1 mm. In one embodiment, the sealing width is from about 0.2 to less than 1 mm.

[0014] In addition, spacer particles 680 are deposited on the device region to prevent the cap from contacting the OLED cells. In one embodiment, the spacer particles comprise a spherical shape. Spacer particles having other geometric shapes, such as cubical, prism, pyramidal, or other regular or irregular shapes are also useful. The average mean diameter of the spacer particles should be sufficient to maintain the desired height of the cavity, which for example is about 2-50 μm. The size and shape distribution of the spacer particles should also be sufficiently narrow to ensure proper separation between the cap and OLED cells.

[0015] FIGS. 3-8 show a process for fabricating an OLED device in accordance with one embodiment of the invention. Referring to FIG. 3, a substrate 360, which serves as an encapsulation cap, is provided. The substrate can comprise various types of materials, such as metal or polymer. The thickness of the substrate can be, for example, 0.4-2 mm. Providing a thin substrate (0.01-0.2 mm) is also useful, particularly for fabricating flexible devices.

[0016] A device layer 380 from which the sealing dam is formed is deposited on a major surface of the cap. In one embodiment, the device layer comprises a non-conductive photosensitive material, such as photoresist. Due to the fine geometry, the dam materials must either be directly or indirectly patternable. Other electrically insulating photosensitive materials, such as photopatternable polyimide, photopatternable polybenzoxazole, photopatternable polyglutarimide and other resins, are also useful. The height of the dam (e.g. 1 um) is larger than the height of the device layer (ca. 0.5 um).

[0017] Referring to FIG. 4, the device layer is patterned to form a sealing dam 280. The patterning process includes, for example, selectively exposing the resist layer followed by a development process to remove the selected portions (i.e., exposed or unexposed portions are removed depending on the use of a positive or negative resist layer). In one embodiment, the sealing dam is formed a distance from the edge of the substrate 260, leaving a sealing region 285. Typically the sealing region is about 0.2-2 mm wide. The dam and substrate form a cap 260 to encapsulate the OLED device.

[0018] Alternatively, non-photosensitive materials that are non-conductive, such as spin-on glass, polyimide, polybenzoxazole, polyglutarimide, or benzocyclobutene, can be used to serve as the sealing dam layer. Other non-photosensitive materials such as polymers, including polyethylene, polystyrene, polypropylene or inorganic materials such as silicon oxide, silicon nitride, aluminum oxide are also useful. For non-photosensitive materials, an etch mask, such as resist, is provided for patterning the device layer.

[0019] In yet another embodiment, multiple layers are used to form a sealing dam stack. At least the upper most layer which contacts the OLED substrate comprises a non-conductive material. The layers are patterned using, for example, an etch mask to form the sealing dam.

[0020] Referring to FIG. 5, a substrate 501 is provided on which OLED cell or cells are formed. The substrate can comprise various types of materials, such as glass or polymer. Other materials which can adequately support the OLED cells are also useful.

[0021] In one embodiment, the substrate comprises a flexible material, such as a plastic film for forming a flexible device. Such films, for example, include transparent poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(enthylene naphthalate) (PEN), polycarbonate (PC), polyimides (PI), polysulfones (PSO), and poly(p-phenylene ether sulfone) (PES). Other materials such as polyethylene (PE), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS) and poly(methyl methyleacrylate) (PMMA), can also be used to form the substrate. A flexible substrate comprising thin glass or other flexible materials is also useful.

[0022] A conductive layer 505 is deposited on the substrate. The substrate can be provided with a barrier layer, such as silicon dioxide (SiO₂), beneath the conductive layer on the substrate surface prior to depositing the conductive. Barrier layers are particularly useful for substrates comprising soda lime glass. The barrier layer, for example, is about 20 nm thick. In one embodiment, the conductive layer comprises a transparent conductive material, such as indium-tin-oxide (ITO). Other types of transparent conductive layers, including zinc-oxide and indium-zinc-oxide, are also useful. Various techniques, such as chemical vapor deposition (CVD) physical vapor deposition (PVD), and plasma enhanced CVD (PECVD), can be employed to form the device layer. The conductive layer should be thin to reduce optical absorption and negative impact on subsequent film formation while satisfying electrical requirements. The conductive layer is typically about 0.02-1 μm thick.

[0023] The conductive layer 505 is patterned as desired to selectively remove portions of the layer, exposing portions 556 of the substrate. The patterned conductive layer serves as first electrodes for the OLED cells. In one embodiment, the conductive layer is patterned to form strips that serve as, for example, anodes of a pixelated OLED device. The patterning process can also form connections for bond pads. Conventional techniques, such as photolithography and etching, can be used to pattern the conductive layer. Patterning techniques using a stamp are also useful. Such techniques are described in co-pending international patent application titled “Mechanical Patterning of a Device Layer” (attorney docket number 99E 8062), which is herein incorporated by reference for all purposes.

[0024] One or more organic functional layers 510 are formed on the substrate, covering the exposed substrate portions and conductive layer. The functional organic layers comprise, for example, conjugated polymer or low molecular materials such as Alq₃. Other types of functional organic layers are also useful. The organic functional layers can be formed by conventional techniques, for example, wet processes such as spin coating or vacuum sublimation (for Alq3 organic layers). The thickness of the organic layers is typically about 2-200 nm.

[0025] Referring to FIG. 6, portions of the organic layers can be selectively removed to expose underlying layers in regions 670 for bond pad connections. Selective removal of the organic layers can be achieved using, for example, a polishing process. Other techniques, such as etching, scratching, or laser ablation, are also useful.

[0026] In one embodiment, spacer particles are randomly distributed on the substrate. Preferably, the spacer particles are randomly distributed in the cell region in which OLED cells are formed. The spacer particles occupy active and non-active parts (e.g., emitting and non-emitting areas) of the device. The distribution or density of the spacer particles should be sufficient to prevent the cap from contacting the OLED cells in the presence of mechanical stress, whether by designed (flexible devices) or accident (handling of the devices). The distribution can be varied to accommodate design requirements, such as the thickness of the cap, thickness of the substrate, and amount of device flexibility needed.

[0027] In a preferred embodiment, the spacer distribution is sufficient to maintain the height of the cavity without visibly affecting the emission uniformity of the OLED cells. Typically, a spacer distribution having an average distance between spacer particles of about 10-500 um is adequate in preventing the cap from contacting the OLED cells. In one embodiment, the density of the spacer particle distribution is about 10-1000 No/mm². Such a distribution along with the small size of the spacer particles ensures that their influence on emission uniformity is essentially invisible to the unaided human eye.

[0028] To avoid causing shorts between the anode and the cathode, the spacer particles preferably comprise a non-conductive material. In one embodiment, the spacer particles are made of glass. Spacer particles made of other types of non-conductive materials, such as silica, polymers, or ceramic, are also useful.

[0029] In one embodiment, the spacer particles are deposited by spraying techniques. In a preferred embodiment, a dry spray technique is employed to deposit the spacer particles. Dry spray techniques are described in, for example, Birenda Bahadur (Ed), Liquid Crystals: Applications and Uses, Vol. 1 (ISBN 9810201109), which is incorporated by reference for all purposes. The area on which the dam is located is cleaned of spacer particles, using a laser cleaning method, or any other suitable method to remove the particles, like scratching or patterning with photoresist.

[0030] Dry spray techniques typically comprise electrostatically charging the spacer particles with a first polarity (positive or negative) and the substrate with a second polarity (negative or positive). The spacer particles are blown against the substrate with dry air supplied by a dry air sprayer. Dry air sprayers, such as a DISPA-μR from Nisshin Engineering Co., can be used. Electrostatic attraction causes the spacer particles to adhere to the substrate while electrostatic repulsion between the particles prevents particle agglomeration on the substrate.

[0031] The use of a wet spray technique to deposit the spacer particles on the substrate is also useful. Wet spray techniques are described in, for example, Birenda Bahadur (Ed), Liquid Crystals: Applications and Uses, Vol. 1 (ISBN 9810201109), which is already incorporated by reference for all purposes. Typically, the spacer particles are suspended in an alcoholic or aqueous liquids, such as ethanol, isopropanol, or a mixture comprising alcohol and water. The spacer concentration, for example, is about 0.1-0.5% by weight. Ultrasonic waves can be used to disperse the particles to prevent agglomeration. For example, the spacer particles can be irradiated with ultrasonic waves for several minutes prior to particle deposition. The prepared suspension is sprayed with air through a nozzle onto the substrate, depositing the spacer particles thereon.

[0032] Referring to FIG. 7, a second conductive layer 715 is deposited on the substrate, covering the spacer particles and other layers formed thereon. The conductive layer comprises, for example, a metallic material such as Ca, Mg, Ba, Ag or a mixture or alloy thereof. Other conductive materials, particularly those which comprises a low work function, can also be used to form the second conductive layer. In one embodiment, the second conductive layer is patterned to form electrode strips that serve as cathode for a pixelated OLED device. Also, connections for bond pads can be formed during the patterning process. Alternatively, the conductive layer can be selectively deposited to form cathode strips and bond pad connections. Selective deposition of the conductive layer can be achieved with, for example, mask layers. The cathode strips are typically orthogonal to the anode strips. Forming cathode strips that are diagonal to the anode strips is also useful. The intersections of the top and bottom electrode strips form organic LED pixels.

[0033] Referring to FIG. 8, the cap 260 is mounted on the substrate with the OLED pixels, aligning the sealing dam to surround the cell region of the OLED device. Pressure is applied to the cap and/or substrate to press them together to avoid the sealant creeping into the gap between the sealing dam and the substrate. A sealant 287 is applied on the substrate around the cap. The sealant, for example, comprises uv-curable epoxy. Other types of sealants such as heat curable epoxy or acrylates are also useful. The sealant creeps in to fill the sealing region 285 between the cap and substrate. The sealant, for example, is cured (e.g., UV or thermal), thus hermetically sealing the OLED device 200.

[0034] The cap creates a cavity 845, providing separation between it and the OLED cells. During the mounting process, the spacer particles may be pressed into the layers of the OLED cells. The spacer particles provide support for the cap over the area of the OLED cells, preventing the cap from contacting the active components of the device when pressure is applied to the cap.

[0035] As described, the process deposits the spacer particles after formation of the organic layers. The spacer particles can alternatively be deposited at other points in the process flow. For example, the spacer particles can be deposited before the formation of the first conductive layer or before the formation of the organic layers. In effect, the spacer particles can be deposited at any point of the process prior to the formation of the second conductive layer.

[0036] The process forms a sealing dam on the cap, as described in FIGS. 3-4. Alternatively, the sealing dam can be formed on the substrate. The dam is formed after the formation of the first conductive layer, but before the formation of the organic functional layer and the deposition of spacer particles.

[0037] While the invention has been particularly shown and described with reference to various embodiments, it will be recognized by those skilled in the art that modifications and changes may be made to the present invention without departing from the spirit and scope thereof. The scope of the invention should therefore be determined not with reference to the above description but with reference to the appended claims along with their full scope of equivalents. 

What is claimed is:
 1. A device comprising: a substrate having a cell region; a sealing dam surrounding the cell region; a cap supported by the sealing dam; spacer particles in the device region to support the cap; a sealing region abutting an outer surface of the sealing dam; and an adhesive located in the sealing region, the adhesive hermetically sealing the device, wherein the sealing dam reduces a sealing width of the device.
 2. The device of claim 1 wherein the cell region comprises one or more OLED cells.
 3. The device of claim 2 wherein the sealing dam comprises a non-conductive material.
 4. The device of claim 3 wherein the sealant comprises a thermally cured adhesive.
 5. The device of claim 1, 2, 3 or 4 wherein the spacer particles comprise a non-conductive material.
 6. The device of claim 5 wherein the spacer particles comprises a mean diameter to maintain a height of the cavity between the cap and substrate.
 7. The device of claim 6 wherein the spacer particles comprise a density to maintain the cavity.
 8. A method for forming a device including encapsulating the device comprising: providing a substrate including a cell region; depositing spacer particles on the substrate; providing a cap with a sealing dam; mounting the cap on the substrate, wherein the sealing dam surrounds the cell region and forms a sealing region abutting an outer surface of the sealing dam and the cap forms a cavity in the device region supported by spacer particles; exerting a pressure to ensure the sealing dam contacts the substrate; and applying an adhesive in the sealing region, the adhesive hermetically sealing the substrate, wherein the sealing dam eliminates a gap between the substrate and the cap to reduce a sealing width of the device.
 9. The method of claim 8 wherein providing the substrate includes forming OLED cells in the cell region of the substrate.
 10. The method of claim 9 wherein the substrate is prepared with a conductive layer patterned to form first electrodes and at least one organic functional layer over the conductive layer.
 11. The method of claim 10 wherein the spacer particles comprise a non-conductive material.
 12. The method of claim 8 wherein depositing the spacer layers comprises dry spraying.
 13. The method of claim 12 wherein the dry spraying comprises: electrostatically charging the substrate with a first polarity and the spacer particles with a second polarity; and blowing the spacer particles against the substrate with dry air.
 14. The method of claim 8 wherein depositing the spacer layers comprises wet spraying.
 15. The method of claim 8, 9, 10, 11, 12, 13 or 14 wherein spacer particles are randomly deposited on the substrate.
 16. The method of claim 15 further comprises removing spacer particles from non-device region of the substrate to make space for the dam.
 17. The method of claim 8 wherein providing the cap with the dam comprises forming a sealing dam on a cap substrate.
 18. The method of claim 17 further comprises curing the adhesive.
 19. The method of claim 18 wherein forming the sealing dam comprises: depositing a device layer on the cap substrate; and patterning the device layer to form the sealing dam on the cap substrate.
 20. The method of claim 19 wherein the sealing dam comprises a photosensitive material.
 21. A method for forming a device including encapsulating the device comprising: providing a substrate including a cell region; forming a sealing dam on the substrate, the sealing dam surrounds the cell region; depositing spacer particles on the substrate; mounting a cap on the sealing dam, wherein a sealing region abuts an outer surface of the sealing dam; exerting a pressure to ensure the cap contacts the sealing dam; and applying an adhesive in the sealing region, the adhesive hermetically sealing the substrate, wherein the sealing dam eliminates a gap between the cap and the substrate to reduce a sealing width of the device.
 22. The method of claim 21 wherein providing the substrate includes forming OLED cells in the cell region of the substrate.
 23. The method of claim 22 wherein forming the sealing dam comprises: depositing a device layer on the substrate; and patterning the device layer to form the sealing dam on the substrate.
 24. The method of claim 23 wherein the device layer comprises a photosensitive layer.
 25. The method of claim 24 further comprises curing the adhesive.
 26. The method of claim 21, 22, 23, 24 or 25 wherein the sealing dam comprises a photosensitive material.
 27. The method of claim 26 wherein the spacer particles comprise a non-conductive material.
 28. The method of claim 21 wherein depositing the spacer layers comprises dry spraying.
 29. The method of claim 28 wherein the dry spraying comprises: electrostatically charging the substrate with a first polarity and the spacer particles with a second polarity; and blowing the spacer particles against the substrate with dry air.
 30. The method of claim 21 wherein depositing the spacer particles comprises wet spraying. 